Weathering The breaking down and changing of rocks at or near the Earth’s surface 2 Types: Mechanical Chemical

Mechanical Weathering Occurs when physical forces break rock into smaller and smaller pieces without changing the rock’s mineral composition Mechanical weathering increases surface area

Three processes that cause mechanical weathering Frost Wedging caused by the expansion of freezing water in cracks and crevices. wedged loose rocks may tumble into large piles called talus, found at the bases of steep, rocky cliffs

Three processes that cause mechanical weathering 2. Unloading/Exfoliation Reduced pressure on igneous rock causes it to expand and allows slabs of outer rock to break off in layers in a process called exfoliation

Three processes that cause mechanical weathering 3. Biological Activity The activity of organisms, including plants, burrowing animals, and humans

Chemical Weathering Is the transformation of rock into one or more new compounds

Processes of chemical weathering Water (dissolved gases) oxygen (Fe + O2 = rust!) CO2 (carbonic acid) sulfur/nitrogen oxides (acid rain)

Erosion Erosion – major external process: loosened material is dissolved, or worn away from one part of the Earth's surface and deposited in another Streams – the most important agent of erosion produce ordinary valleys and canyons; may form deltas when they flow into lakes and oceans Wind Erosion – produces dunes or loess Human activities can accelerate erosion: activities that destroy vegetation